Radio receiving apparatus



Nov. 14, 1933. M. w. KENNEY RADIO RECEIVING APPARATUS Filed May 10, 1929Patented Nov. 14, 1933 1 Q 11 11 STAT-ES PATENTI'OFFICE 7 r 1,935,401RADIO RECEIVING APPARATUS Mahlon W. Kenney, Elmliurst, Ill. ApplicationMay 10, 1929. Serial No. 361,847

7 Claims. 01. 179-171 trolling resistance mounted upon the endof thecondenser shaft, and

Fig. 3 is an end view of the variable resistance element for thebiascontrol.

In the drawing an antenna 11 is shown leading 60 to avariable resistanceor potentiometer 12 upon which the incoming signals are impressed. Thepotentiometeris shunted by a condenserlB forming a capacitative couplingbetween the resonant input circuit comprising a variable inductance 14and a variable condenser 15. The signals from this circuit are impressedupon the grid [16 of a thermionic relay 17 of the hot cathode type. Theradio frequency signals are successively This invention relates to 'aradioreceiving a paratus and more particularly to means for maintaininguniform sensitivity in a radio receiver in the reception of waves ofdifferent fre- "6 quencies.

In a'reception of radio frequency waves, it is found that theradio'frequency transformers do not uniformly step up the voltages forthe different frequencies, due chiefly to the following two things?First, the magnetic coupling at the higher frequencies is greater thanat the lower frequencies. Second, the L/C. ratio becomes greater. at thehigh frequencies than at the low frequencies. These facts areparticularly disturbing in tuned radio frequency amplifiers, be cause inorder to get'enough amplification at the low frequencies, several stagesare necessary.

- This, then, is' accompanied by an extremely high amplification at thehigh frequencies, which, for 20 a number of reasons, becomes almostuncontrollable, even in a well shielded receiver. If, therefore, thereceiving set has its sensitivity automatically-adjusted, as the maintuning control is turned; the receiver can be made to show equal; oralmost any degree of sensitivity over the entire frequency band, andalso be exceptionally free from regeneration because of the reduction ofthe: extreme amplification at the high frequencies.

1 An object of the invention is to provide an improved radio receivingapparatus. f

A further object is to provide a radio receiving apparatus having auniform or predetermined sensitivity for different frequencies.

'A further object is to provide an apparatus for automatically adjustingthe sensitivity of a radio receiver inaccordance with the frequency towhich the receiver is adjusted.

A further object is to provide anapparatus for varying the platecircuitresistance in accordance 19 and 21 which are connected in cascade tothermionic relays 22, 23 and 24, each transformer having a'fixedcondenser 25 and a variable condenser 26 across its secondary winding.Relay 24 servesas a detector and is provided witha grid condenser27 andleak resistance 28. In order to control the feed back or regeneration, adegenerating condenser 29 is connected between the grid of each relayand one end of the secondary winding of the radio frequency transformerin the output circuit of the relay. A potential varying oppositely tothe grid potential is impressed upon the condenser29 by a reactance coil31 which is connected to the end of the secondary winding of thetransformer and lead's'to ground 32. r The degree of amplification ofthecircuit may be regulated by placing the variable resistance 34between cathodes 33 and the negative side of the B batterysupply. ,Theeffect of this resistanceis to render the cathodes positive withrespectto the grids, producing a negative bias upon the grids.' Anadditional effect of this resistance is to changethe internal plateimpedance of the tube, thereby changing the sensitivity of each in:

transferred to radio frequency transformers 18, 70 7 with the frequencyto which the receiver is adjustedv 1 A further object is to provide anapparatus for controlling the outputcircuit of an audion in a tunedradio frequency circuit in accordance with the condenser setting of theinput circuit.

A further object is to provide an apparatus for varying the grid bias inaccordance with the frequency for which the apparatus is in resonance.

Referring to the drawing:

Fig. 1 is a diagrammatic view of a radio receiver embodying theinvention;

Fig. 2 is a fragmentary plan view of the gang condenser of the apparatusshowing the bias condividual stage, and likewise the over-allsensitivity of the receiver. It also adds resistance to the platecircuits ofthe tubes and reduces the potential of the B supply. Thevariable resistance, 34.

may be omitted and the, volume may be con:

trolled wholly by the potentiometer 12.

An auxiliary control resistance 35 is provided between the main volumecontrol resistance 34 and the cathodes, or in case the main volumecontrol resistance is omitted,'the auxiliary re- 135 sistance isconnected directly to the negative side of the B supply.

All of the variable condensers l5 and 26 are mounted upon a single shaft36, which is mounted in a frame 3'7. The end of the shaft 36 is providedwith a bore 38 into which a stub shaft 39 is inserted and held in placeby a set screw 41. The stub shaft 39 carries an arm 42 and serves toengage a flexible element 43 with a resistance element 35 to placevarying portions of the resistance in the circuit between the cathodesand the B supply as the arm is rotated. The resistance element issupported in an insulating cup 44 which is stationarily mounted upontheframe 3'7. Thus as the position of condensers 15 and 26 is changed totune the receiver to receive different frequencies the resistance willautomatically be changed. For high frequencies a large amount ofresistance will be placed in the circuit making the grids more negativewith respect to the c'athodes and for low frequencies the resistancewill be decreased. The value of the resistance is so chosen that thetransformer will have a substantially flat characteristic curve ofamplification for a different frequencies indicating that the degree ofamplification for all frequencies is substantially uniform. Since thedegeneration produced by condensers 29 and coils 31 varies for differentdegrees of amplification it will be seen that if the apparatus isadjusted to produce the proper amount of degeneration at one frequencyto render it stable this adjustment will not be disturbed when theapparatus is tuned to receive waves of a different frequency.

of frequency characteristic over the entire broadcast frequency band.This is accomplished by controlling the rate of change of resistanceasthe main tuning dial is turned.

It will be understood that the embodiment of the invention hereindescribed is merely illustrative and that many other modifications maybe devised by those skilled in the art without departing from the spiritand scope of theinvention.

What I claim as new and desire to protect by United States LettersPatent is:

1. In a radio receiver, a plurality of thermionic relays each having agrid circuit and a plate circuit, an electron emission element in eachplate circuit, a condenser in each grid circuit for tuning the gridcircuit, a shaft for actuating all of said condensers, means fornegatively biasing said grids relative to said elements increasing thenegative bias for high frequencies and decreasing the negative bias forlow frequencies, said biasing means being mounted on the condensershaft.

2. In a radio receiver, a plurality of thermionic relays each having agrid circuit and a plate circuit, an electron emission element in eachplate circuit, a condenser in each grid. cir i for tuning the gridcircuit, a support for said condensers, a common shaft for varying theadjustment of said condensers to tune said circuits for variousfrequencies, a common resistance element for applying a negative gridbias to vary the grid bias of said relays, said resistance element beingmounted upon the condenser support, an arm carried by said condensershaft and operable to vary theresistance in accordance with the positionof said shaft whereby the tuning'of the grid circuit and the grid biaswill have a predetermined relation.

3. In a receiving system, a thermionic relay having an anode, a'grid,and a cathode, an anode circuit, a grid circuit, means for compensatingfor the interelectrode capacity of said relay to prevent feed-back ofenergy from the anode to the grid'circuit, means for applying a positivepotential to the cathode relative to the grid, and means for varyingsaid positive potential to maintainuniform sensitivity in the system.

4. In a radiofrequency amplifier. having'a' vacuum tube provided withinput and output circuits, means to tune at least one of said circuitsto adjust the frequency response thereof, said circuit havinganon-uniform transmission characteristic over its frequency operatingrange, volume control means for adjusting the amplifies.- tion of saidtube'by varying the relative potentials of the cathode and controlelectrode of said tube, and means for adjusting said volume controlmeans inlresponse to the tuning adjustment whereby the over-allsensitivity of theamplifier at various frequencies is substantiallyconstant. 5. In a radio' frequency amplifier having .a vacuum tubeprovided with input and output circuits, transformers in said circuits,tuning means for one of said circuits to adjustthe frequency response,means for negatively biasing the control electrode'with respect to thecathode of said tube, and means forchanging saidcontrol electrode biaswith said tuning adjustment so that as the resonance frequency isincreased the sensitivity of the amplifier isdecreased to compensate forthe increasedtransmission characteristic of the circuits.

6. In a radio frequency amplifier having a vac uum tube provided withinput and output circuits, tuning means in saidinputgcircuit for adjusting the frequency response, means for maintaining the potential ofthe cathode positive-with respect to the control electrode, and meansfor varying, said positive potential in accordance with the tuningadjustment, so that the amplification-of the tube is varied in 'a'senseoppositeto the variation in transmission characteristics of the inputand output circuits whereby a uniform over-all sensitivity of theamplifier for varying frequencies is obtained. r

7. The circuit of claim 4 in which the volume control means comprises amain volume control and an auxiliary volume control with the aux iliarycontrol adjusted in response to tuning adjustments.

. MAHLON W.

